Ultrasonic device for tissue ablation and sheath for use therewith

ABSTRACT

A transverse mode ultrasonic probe is provided which creates a cavitation area along its longitudinal length, increasing the working surface of the probe. Accessory sheaths are also provided for use with the probe to enable a user to select from features most suited to an individual medical procedure. The sheaths provide acoustic enhancing and aspiration enhancing properties, and/or can be used as surgical tools or as medical access devices, protecting tissue from physical contact with the probe.

This is a continuation-in-part of Provisional Application No.60/157,824, filed Oct. 5, 1999; No. 60/178,901, filed Jan. 28, 2000 andapplication Ser. No. 09/618,352, filed Jul. 19, 2000.

FIELD OF THE INVENTION

The present invention relates generally to a shielded ultrasonic medicalprobe operating in a transverse mode for ablating and removing undesiredtissue. In particular, the invention provides one or more acousticalsheaths for use with the probe, allowing the user to control and focusthe energy emitted by the probe in a manner most suited to the desiredmedical procedure.

BACKGROUND OF THE INVENTION

Ultrasonic energy has been considered for tissue ablation andfragmentation of plaque and thrombosis for removal of intravascularocclusions due to atherosclerotic plaque and intravascular blood clots.Surgical devices utilizing ultrasonic probes for generation andtransmission of ultrasonic energy, have been disclosed in the art (U.S.Pat. Nos. 5,112,300; 5,180,363; 4,989,583; 4,931,047; 4,922,902; and3,805,787). Typically, the energy produced by an ultrasonic probe is inthe form of very intense, high frequency sound vibrations, results infragmentation of tissue (palque and thrombosis) either as a result ofmechanical action thereon or “cavitation” thereof, in which high energyultrasound frequency applied to liquids generates vapor-filledmicrobubbles or “cavities” with the concomitant rapid expansion andcollapse of the cavites that is accompanied by intense localizedhydraulic shock, that causes fragmentation or dissolution of the tissue.Medical applications for ultrasonic probes providing cavitation includesurgical procedures for ablation of tissues, for example, treatment ofcancer, tissue remodeling, liposuction, and removal of vascularocclusions. Typically, ultrasonic probes described in the art for use insurgical procedures include a mechanism for irrigating an area where theultrasonic treatment is being performed (e.g., a body cavity or lumen)to wash tissue debris from the area, and may further include anaspiration means to remove irrigation fluid and tissue debris from thesite of the procedure. Mechanisms used for irrigation or aspirationdescribed in the art are generally structured such that they increasethe overall cross-sectional profile of the probe, by including inner andouter concentric lumens proximal to or within the probe to provideirrigation and aspiration channels. In addition to making the probe moreinvasive, prior art probes may also maintain a strict orientation of theaspiration and the irrigation mechanism, such that the inner and outerlumens for irrigation and aspiration remain in a fixed position relativeto one another, which is generally closely adjacent the area oftreatment. Thus, the irrigation lumen would not extend beyond thesuction lumen (i.e., there is no movement of the lumens relative to oneanother) and any aspiration would be limited to picking up fluid and/ortissue remnants within the defined distance between the two lumens.

Ultrasonic probes described in the art for tissue ablation suffer from anumber of limitations. Such probes depend on longitudinal vibration ofthe ultrasonic member comprising the probe i.e. vibration of the probein the direction of the longitudinal probe axis to effect tissuefragmentation. Probe action in this modality therefore depends primarilyon mechanical and thermal action of the probe tip for disrupting tissue,since the cavitational energy emanating from the tip, especially innarrow diameter probes such as those used to remove vascular occlusions,is minimal due to the small surface area of the tip itself. This primarymode of action imposes the following limitations on probe efficiency:

i) tissue ablation is restricted to very small area defined by thesurface area of the probe tip, thereby necessitating time consumingsurgical procedures to remove relatively large occluded areas with bloodvessels in comparison to instruments which excise tissue by mechanicalcutting, electrocautery, or cryoexcision methods.

ii) occurance of late restenosis (typically within three months), and toa lesser extent acute re-occlusion after coronary angioplasty are majorclinical problems limiting the long-term efficacy of ultrasonic surgicalprocedures for treatment of atherosclerosis and coronary angioplasty.While the pathogenosis of restenosis is still unclear, it has beendemonstrated from autopsy specimens from patients with restenosis thepathophysiologic process leading to acute occlusion after coronaryangioplasty is related either to a thrombotic mechanism or to majorplaque dissection and superimposed thrombosis, and that these eventsleading to chronic restenosis involves vascular injury, plateletdeposition and thrombosis and connective tissue synthesis. Such postoperative processes are typically result from localized trauma at thesurgical site caused by mechanical and thermal action of longitudinallyvibrating probes.

Attempts to reduce some of the aforementioned problems associated withlongitudinally vibrating probes have been disclosed in the art, whereinthe primary action of the probe through longitudinal vibration issupplemented by a limited, supplementary transverse vibration of theprobe tip i.e. perpendicular to the longitudinal axis of the probe. Itis proposed that such secondary transverse vibrations in these probeswill result in increased efficiency for surgical procedures. Forexample, U.S. Pat. No. 4,961,424 to Kubota, et al. discloses anultrasonic treatment device that produces both a longitudinal andtransverse motion at the tip of the probe. The Kubota, et al. device,however, still relies solely on the tip of the probe to act as a workingsurface. Thus, while destruction of tissue in proximity to the tip ofthe probe is more efficient, tissue destruction is still predominantlylimited to the area in the immediate vicinity at the tip of the probe.U.S. Pat. No. 4,504,264 to Kelman discloses an ultrasonic treatmentdevice, which improves the speed of ultrasonic tissue removal byoscillating the tip of the probe in addition to relying on longitudinalvibrations. Although tissue destruction at the tip of the device is moreefficient, the tissue destroying effect of the probe is still limited tothe tip of the probe. Both probes described in Kubota, et al., andKelman, et al., are further limited in that the energy produced at thetip of the probe is unfocused, the action of the probe tends to push thetissue debris ahead of the probe tip. Likewise, the concentration ofenergy solely at the probe tip results in heating of the probe tip,which can create tissue necrosis, thereby complicating the surgicalprocedure and potentially compromising the recovery of the patient.Furthermore, such probes do not eliminate the problems associated withlongitudinally vibrating probes.

The aforementioned limitations associated with longitudinally vibratingprobes can be overcome entirely by utilizing an ultrasonic probe thatvibrates exclusively in the transverse mode. Such probes are capable ofgenerating substantially higher cavitational energy through a pluralityof nodes along the entire longitudinal axis of the vibrating probe,thereby eliminating the need for mechanical and thermal action at theprobe tip. The advancing probe tip can therefore be shielded to preventmechanical injury to the walls of the blood vessel for example, therebyprecluding scarring, platelet deposition and clotting that lead torestenosis. Additionally, such probes are capable of tissuefragmentation over greater surface area (along the entire longitudinalaxis) resulting in high efficiency, thus allowing for rapid surgicalprocedures and substantially eliminating thermal effects on tissuecaused by prolonged probe operation.

Since probe vibrating exclusively in a transverse mode is entirelydependent on cavitational energy for their action, important factors formaintaining efficiency of such probes are (i) narrow probe diameter tofacilitate oscillation at lower ultrasonic energies and (ii) increasedlogitudinal axis (probe length) that results in more cavitation nodes.Although narrow probe diameters are advantages especially fornegotiation through narrow blood vessels and occluded arteries, theutilization of such probes have been precluded by inability toeffectively control the vibrational amplitude of thin probes, thatresult in potential damage to the probe and greater risk of tissuedamage resulting from their use. The use of narrow diameter probes havebeen disclosed in the art for providing greater maneuverablility ease ofinsertion in narrow blood vessels. U.S. Pat. No. 4,920,954 to Allingerdiscloses a narrow diameter ultrasonic device wherein a rigid sleeve isused to prevent transverse vibrations U.S. Pat. No. 5,380,274 disclosesa narrow diameter probe for improved longitudinal vibration having asheath to inhibit transverse vibration U.S. Pat. No. 5,469,853 to Lawdiscloses a thin, longitudinally vibrating ultrasonic device with abendable sheath that facilitates directing the probe within narrow bloodvessels. While the prior art has focused on the need for using sheathson thin ultrasonic devices, their use has been entirely to preventtransverse vibrations of the device and to protect such devices fromdamage resulting from such vibrations.

Based on the aforementioned limitations of ultrasonic probes in the art,there is a need for ultrasonic probe functioning in a transverse modethat further obviates the shortcomings of that further overcomeslimitations imposed by of narrow diameter requirements for efficientoperation of such probes for rapid tissue ablation. Transverselyvibrating ultrasonic probes for tissue ablation are described in theApplicant's co-pending provisional applications U.S. Ser. Nos 60/178,901and 60/225,060, and Ser. No. 09/776,015 which further describe thedesign parameters for such a probe its use in ultrasonic devices fortissue ablation. The entirety of these applications are hereinincorporated by reference.

There is a further need for controlling the for procedures which requireprecise delivery of cavitation energy to defined locations, to be ableto resttrict the cavitation energy emanating circumferentially from atransversely vibrating p at multiple nodes wastes a portion of theenergy given off by the probe, as the energy is unfocused and dispensedalong the length of the probe.

There is also a need in the art for a means of focussing thecavitational energy emitted by such a probe to deliver the energy toexactly to the desired location within a blood vessel while shieldingthe surrounding tissue from damage.

SUMMARY OF THE INVENTION

The present invention is directed towards a transversely vibratingultrasonic probe for tissue ablating surgical devices that overcomes theaforementioned limitations of ultrasonic probes in the art used for thisapplication. Particularly, the present invention is directed towardsproviding a means to control, direct and focus the cavitation energyfrom a transversely vibrating ultrasonic probe by utilizing a sheathassembly extending circumferentially along the longitudinal axis of theprobe. In accordance with the present invention, there is provided anultrasonic probe operating in a transverse mode whereby the probe iscable of vibrating in a direction perpendicular to its longitudinal axisupon application of an ultrasonic frequency, capable of preciselyfocussing or directing the cavitation energy of the probe to definedregions within a blood vessel. The object of this invention can beaccomplished by a transversely vibrating ultrasonic probe described in aco-application submitted by the applicants U.S. Ser. No. 09/776,015, theentirety of which is herein incorporated by reference.

Further in accordance with the invention, a sheath, a sleeve or otherdamping member provided with fenestrations is a a sheath that is adaptedcircumferentially along the probe axis, thereby providing control overrelease of cavitation energy in specific regions along the probe axis.Non-fenestrated areas of the said sheath or sleeve effectively blockcavitation energy emanating from the probe from such areas.

Still further in accordance with the invention, a sheath assemblycomprising one or more sheaths may can be adapted to the ultrasonicprobe, thereby providing a means of containing, focussing, andtransmitting energy generated along the length of the probe to one ormore defined locations. The sheaths of the present invention alsoprovide the user with a means of protecting regions of tissue fromphysical contact with the probe. In one embodiment of the invention hesheaths also comprise a means for aspiration and irrigation of theregion of probe activity, as well as a means of introducing a drug orcompound to the site of probe activity.

In one aspect, a plurality of sheaths are used in combination to provideanother level of precision control over the direction of cavitationenergy to a tissue in the vicinity of the probe. In one embodiment ofthe invention, the sheath encloses a means of introducing fluid into thesite of the procedure, and a means for aspirating fluid and tissuedebris from the site of the procedure. In another aspect the sheathassembly further encloses a means of introducing a drug intravascularlythat dissolves clots and prevents the recurrence of stenosis. Theultrasonic oscillation of the probe of the present invention will beused to facilitate the penetration of antithrombogenic agents into thevascular or luminal walls to inhibit restenosis. Preferredantithrombogenic agents include heparin, hirudin, hirulog, urokinase,streptokinase, tPA, and similar agents. In a further embodiment, theprobe tip can be moved within the sheath. In yet another aspect, theirrigation and aspiration means, and the probe tip, can all bemanipulated and repositioned relative to one another within the sheath.In another embodiment, the sheath is shaped in such a way that it maycapture or grasp sections of tissue that can be ablated with the probe.

Still further in accordance with the invention, the sheath provides aguide for the probe tip, protecting tissues from accidental puncture bythe sharp, narrow-diameter tip, or from destruction by energy emittedradially from the probe during,introduction of the probe to the site.The sheath may be applied either to the probe tip prior to insertion ofthe probe into the patient, or pre-inserted into the patient prior tothe insertion of the probe. The sheath of the present invention can beused to fix the location of one or more shapes relative to the nodes oranti-nodes of a probe acting in transverse action. The location of thereflective shapes can amplify the acoustical wave thereby magnifying theenergy. This allows for the use of very small diameter probes whichthemselves would not have the requisite structural integrity to applyand translate acoustical energy into sufficient mechanical energy toenable ablation of tissues. The reflective shapes can also focus orredirect the energy, effectively converting a transverse probe emittingcavitation energy along its length, to a directed, side fire ultrasonicdevice.

In a still further aspect of the invention the probe emits transverseultrasonic energy along its longitudinal axis that may be used to, forexample, fragment abnormal cells on the surface of the body cavity whichcome within the sweep of the probe, or to clear obstructions andconstrictions within vasculature or tissue lumen. The device is designedto have a small cross-sectional profile, which also allows the probe toflex along its length, thereby allowing it to be used in a minimallyinvasive manner. In one aspect, the probe be at least partiallycontained within the sheath to contain, focus, intensify, and direct theemitted cavitation energy to specific target tissue sites. In anotherembodiment of the invention, a plurality of sheaths are used incombination to provide another level of precision control over thedirection of cavitation energy to a tissue in the vicinity of the probe.

Still further in accordance with the invention, the sheath encloses ameans of introducing fluid into the site of the procedure, and a meansfor aspirating fluid and tissue debris from the site of the procedure.In a further embodiment, the probe tip can be moved within the sheath.In one aspect, the irrigation and aspiration means, and the probe tip,can all be manipulated and repositioned relative to one another withinthe sheath. In another aspect, the sheath is shaped in such a way thatit may capture or grasp sections of tissue that may be ablated with theprobe. In yet another embodiment, the sheath provides a guide for theprobe tip, protecting tissues from accidental puncture by the sharp,narrow diameter tip, or from destruction by energy emitted radially fromthe probe. The sheath may be applied to the probe tip prior to insertionof the probe into the patient, or the sheath can be inserted into thepatient prior to the insertion of the probe.

The sheath of the present invention can be used to fix the location ofone or more shapes relative to the energy nodes or anti-nodes emitted bya transversely vibrating probe. The location of and the particular shapecan modulate the energy emitted from the probe at one site, andcommunicate it to a distant site, for example, it may amplify theacoustical wave at one or more energetic nodes, thereby increasing theenergy emitted at the sheath's aperture. This allows for the use of verysmall diameter probes which themselves would not have the requisitestructural integrity to apply and translate acoustical energy intosufficient mechanical energy to enable ablation of tissues. Thereflective shapes can also focus or redirect the energy, effectivelyconverting a transverse probe emitting cavitation energy along itslength, to for example, a directed, “side-fire” ultrasonic device.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings, like reference characters generally refer to the sameparts throughout the different views. The drawings shown are notnecessarily to scale, with emphasis instead generally being placed uponillustrating the principles of the invention.

FIG. 1 illustrates an exemplary ultrasonic device comprising theultrasonic probe tip constructed in accordance with the principles ofthe present invention

FIG. 2 shows the areas of maximum vibrations (nodes) and minimumvibrations (anti-nodes) caused by transverse vibration of probe andprobe tip.

FIGS. 3a-g show different configurations of sheaths comprising thesheath assembly adapted to the probe.

FIG. 4 shows a probe that is substantially contained within a sheathcomprising a plurality of fenestrations.

FIG. 5 shows a probe that is substantially contained within a sheathassembly comprising a plurality of adjustable sheaths.

FIG. 6 shows a longitudinal cross-sectional view of the distal end ofthe probe comprising a central irrigation passage, lateral irrigationlumens and external aspiration channels.

FIG. 7 shows a transverse cross-sectional view of a portion of the probeillustrating the irrigation and aspiration channels.

FIG. 8 are longitudinal cross-sectional views of the distal end of theprobe contained within sheaths incorporating angled reflective elements.

FIG. 9 are longitudinal cross-sectional views of the distal end of theprobe contained within sheaths incorporating arctuate of reflectiveelements.

DETAILED DESCRIPTION OF INVENTION

The following terms and definitions are used herein:

“Anti-node” as used herein refers to a region of minimum energy emittedby an ultrasonic probe on or proximal to a position along the probe.

“Cavitation” as used herein refers to shock waves produced by ultrasonicvibration, wherein the vibration creates a plurality of microscopicbubbles which rapidly collapse, resulting in molecular collision bywater molecules which collide with force, thereby producing the shockwaves.

“Cross-sectional diameter” as used herein refers to the diameter of thecylindrical regions of the probe, including the probe tip.

“Fenestration” as used herein refers to an aperture, window, opening,hole, or space. “Node” as used herein refers to a region of maximumenergy emitted by an ultrasonic probe on or proximal to a position alongthe probe.

“Probe” as used herein refers to a device capable of being adapted to anultrasonic generator means, which is capable of propagating the energyemitted by the ultrasonic generator means along its length, and iscapable of acoustic impedance causing transformation of ultrasonicenergy into mechanical energy.

“Sheath” as used herein refers to an apparatus for covering, encasing,or shielding in whole or in part, a probe or portion thereof connectedto an ultrasonic generation means.

“Transverse” as used herein refers to vibration of a probe at rightangles to the axis of a probe. A “transverse wave” as used herein is awave propagated along an ultrasonic probe in which the direction of thedisturbance at each point of the medium is perpendicular to the wavevector.

“Tuning” as used herein refers to a process of adjusting the frequencyof the ultrasonic generator means to select a frequency that establishesa standing wave along the length of the probe.

The present invention provides an ultrasonic medical device for tissueablation. More particularly the present invention provides an ultrasonicdevice comprising a probe capable of vibrating ultrasonically in atransverse mode causing generation of cavitational energycircumferentially around the said probe, comprising a protective sheathassembly adapted over the probe that is capable of focussing, directingand modulating the cavitational energy emitted by the probe. The sheathassembly of the invention allows the user to optimize the tissueablation efficiency of the probe to suit a particular medical procedure.

The probe of the invention is capable of removing tissue at siteswherein the probe makes actual contact with the tissue, and typically ina region that is radially disposed (approximately 2 mm) from the probe,that corresponds to the region of maximum cavitational energy or “nodes”emanating perpendicular to the longitudinal axis of the probe. Byeliminating the axial motion of the probe and allowing transversevibrations only, fragmentation of large areas of tissue spanning theentire length of the probe due to generation of multiple cavitationalnodes along the probe length perpendicular to the probe axis. Sincesubstantially larger affected areas within an occluded blood vessel canbe denuded of the occluded tissue in a short time, actual treatment timeusing the transverse mode ultrasonic medical device according to theinvention is greatly reduced as compared to methods using prior artprobes that primarily utilize longitudinal vibration (along probe axis)for tissue ablation. Because the thinnest region of the probe is capableof providing multiple energy nodes along its length, it is desirable tohave a means of modulating this energy, thereby providing a precise wayof delivering the energy selectively to desired locations, such as forexample an occluded region within a blood vessel, while protectingnearby tissues both from the fragmenting energy and physical damage (forexample, punctures) from the narrow diameter probe tip. The probeequipped with a sheath assembly such as that described herein, providesa means for modulating the intensity and direction of energy emittedfrom such a probe. Additionally, the probe equipped with the sheathassembly of the invention provides a more efficient, selective means ofdelivering energy from the probe to a specific tissue or tissue space,for example at the site of an occlusion within a blood vessel, causingrapid fragmentation and ablation of said tissue without detrimentaleffect other areas within the vessel.

Probes of the present invention are described in the Applicant'sco-pending provisional applications U.S. Ser. Nos. 60/178,901 and No.60/225,060 which further describe the design parameters for anultrasonic probe operating in a transverse mode and the use of such aprobe to remodel tissues. The entirety of these applications are hereinincorporated by reference.

The present invention allows the selective application of cavitationenergy emitted from an ultrasonic probe to tissue. The probe is adaptedto an ultrasonic generator means that selectably provides energy over afrequency range of from about 20 kHz to about 80 kHz. In the currentlypreferred embodiment, the frequency of ultrasonic energy is from 20,000Hertz to 35,000 Hertz. Frequencies in this range are specificallydestructive of hydrated (water-laden) tissues, while substantiallyineffective toward high-collagen connective tissue, or other fibroustissues such as skin or muscle tissues. The amount of cavitation energyto be applied to a particular site requiring treatment is a function ofthe amplitude and frequency of vibration of the probe, as well as thelongitudinal length of the probe tip, the proximity of the tip to atissue, and the degree to which the probe tip is exposed to the tissues.Control over this last variable can be effectuated through the sheath ofthe present invention.

A significant advantage of the ultrasonic medical device of theinvention is that it physically destroys and removes undesired tissuethrough the mechanism of cavitation, which is non-thermal. As aconsequence, the complications which are arise from thermal destructionor necrosis of tissue are not observed. The increase in localtemperature is most likely a result of the heating of the probe. Byusing the probe contained within a sheath of the present invention theprobe is substantially contained and isolated from direct contact withthe tissues, thereby enabling destruction of tissues with only a smallincrease in local temperature, about 7° C. from normal body temperature.The use of a sheath further diminishes or prevents the local temperaturerise. Accordingly, In one embodiment, the sheath of the presentinvention provides a means of insulating surrounding tissue from thethermal side effects of the ultrasonic probe.

The length and diameter of the sheath used in a particular surgicalprocedure is dependent on the type of probe used, the degree to whichthe probe length will be inserted into the patient, and the degree ofshielding that is required based on the specific areas to be treated.For example, in an application whereby prostate tissue is removed via anintra-urethral route with the ultrasonic probe of the present invention,the sheath must be of a sufficient length to protect the tissue of theurethra, of a sufficient outside diameter to facilitate insertion of thesheath into the urethra, and a sufficient inside diameter capable ofaccepting the probe. By contrast, for tissue remodeling near, forexample, the eye, a probe useful for such a procedure would besignificantly shorter and of a significantly smaller diameter, and assuch, so would the sheath. The exact dimensions of the sheath includingits length and diameter is determined by requirements of a specificmedical procedure. Similarly, as illustrated in FIGS. 3 and 4, theposition and size of the sheath aperture 111, or number and positions ofthe fenestrations 111, or the presence of a bevel on the sheath terminus129 to provide a means for tissue manipulations, will likewise bedetermined by the type of procedure, and the requirements of theparticular patient.

In one aspect of the invention, as shown in FIG. 5, the sheath comprisesan inner sheath 121 and an outer sheath 108. The outer sheath may beconnected to a retraction trigger (not shown), by one or morearticulation means, such as wires, which is capable of moving the outersheath with respect to the inner sheath. Each wire comprises a first endand a second end. The first end is affixed to the outer sheath 108,while the second end is affixed to a retraction trigger. When the outersheath 108 is slid back away from the terminus of the inner sheath 121the tissues are exposed to cavitation energy emitted by the probe.

In another embodiment, the sheath is flexible. Articulation wires (notshown) comprising two ends, are connected to the sheath and anarticulation handle. When the articulation handle is manipulated, forexample, pulled axially inward, the flexible sheath will bend orarticulate in a bending or articulation direction A, thereby causing theultrasonic probe to bend or articulate in articulation direction A. Inthis way, the ultrasonic probe can be used to reach locations that arenot axially aligned with the lumen or vessel through which the sheathand probe are inserted.

A particular advantage of the ultrasonic probe operating in transversemode is that the efficient cavitation energy produced by the probedisintegrates target tissue to small particles of approximately 5microns in diameter. Because of the operation of the probe, tissuedebris created at the probe tip is propelled in a retrograde directionfrom the probe tip. Accordingly, in another embodiment of the invention,the sheath provides at least one aspiration channel, which can beadapted to a vacuum or suction device, to remove the tissue debriscreated by the action of the probe. The aspiration channel can bemanufactured out of the same material as the sheath provided it is of asufficient rigidity to maintain its structural integrity under thenegative pressure produced by the aspiration means, for example a vacuumpump or other source of negative pressure. Such an aspiration channel isprovided either inside the lumen of the sheath, or along the exteriorsurface of the sheath, or both. In these embodiments, the aspirationchannel can be a second hollow sheath nested within the first sheath, orthe aspiration channel can be formed in the body of the sheath. Apreferred embodiment is shown in FIGS. 6 and 7, whereby the probe 22itself has one or more grooves defining one or more aspiration channels60, and aspiration of tissue debris is effectuated along the probelength between the interior surface of the sheath and the exteriorsurface of the probe, as directed by the aspiration channels and byretrograde flow from the probe action. FIG. 6 shows a longitudinalcross-section of a portion of an ultrasonic probe 22 and tip 23according to one embodiment of the invention, comprising a centralirrigation passage 17 and lateral irrigation lumens 19, as well asexternal aspiration channels 60. The sheath, not shown, would surroundthe probe.

In another embodiment, the sheath of the present invention comprises anirrigation channel. The sheath is adapted to an irrigation means, forexample, a peristaltic pump or other such device for delivering liquidsunder controlled flow rates and pressures, and the sheath directs fluidto the location of the probe. The irrigation channel can be manufacturedout of the same material as the sheath provided it is of a sufficientrigidity to maintain its structural integrity under the positivepressure produced by the flow of fluid produced by the irrigation means.Such an irrigation channel is provided either inside the lumen of thesheath, or along the exterior surface of the sheath, or both. In theseembodiments, the irrigation channel can be a second hollow sheath nestedwithin the first sheath, or the irrigation channel can be formed in thebody of the sheath. In one embodiment, the probe itself has one or moregrooves defining irrigation channels, and fluid is directed along theprobe length between the interior surface of the sheath and the exteriorsurface of the probe, as directed by the irrigation channels. In thisembodiment, irrigation fluids provide a means of cooling the probe. Thesheath itself, or an irrigation sheath contained within the first sheathcan provide a means of introducing a drug or pharmaceutical formulationto the site of probe activity. For example, anti-thrombolytic drugs suchas heparin, streptokinase, tPA, urokinase, hirulog, or hirudin may beintroduced to the site of a vascular occlusion through the sheath. Theultrasonic energy further provides a means for assisting the drug inpenetrating the occlusion.

In yet another embodiment, the sheath of the present invention furthercomprises both an irrigation and an aspiration channel. As in the aboveembodiments, the channels may be located within the sheath lumen, orexterior to the sheath, or a combination of the two, and can be proximalor distal to the other channel provided they are not in directcommunication. Likewise, in these embodiments the probe itself has aplurality of grooves defining aspiration channels and irrigationchannels, and fluid is directed along the probe length between theinterior surfaces of the sheaths and the exterior surface of the probe,as directed by the aspiration and irrigation channels. In another aspectof the invention, the sheath comprises a means for directing,controlling, regulating, and focussing the cavitation energy emitted bythe probe, an aspiration means, an irrigation means, or any combinationof the above.

In yet another embodiment, as shown in FIG. 8, the sheath is a devicethat allows for the manipulation of tissues, comprising a surface thatis capable of manipulating tissues near the site of the probe. In thisaspect, the terminus of the sheath may be closed, such that the sheathinsulates tissues from the destructive energy emitted by the probe andcan be used to push tissues away from the aperture 111, thereby allowingproximal tissues to be exposed to the probe 22 and 23. Alternatively,the sheath comprises a beveled or arcutate surface at the sheathterminus 129, capable of providing a means for hooking, grasping, orotherwise holding a tissue in proximity to the probe 22 and 23. Inanother embodiment, the sheath allows for the introduction of anothersurgical device, for example, flexible biopsy forceps, capable ofmanipulating tissues into a tissue space, such that the surgical devicecan hold the tissue in proximity with the probe.

In a further embodiment, the internal surface of the sheath provides ameans to amplify or focus cavitation energy from the probe 22. In thisaspect, the interior surface of the sheath comprises at least onestructure or reflective element 118, that extends into the sheath lumen.The reflective element may be planar, or arcutate, or a combination ofthese shapes. Reflective elements of the present invention may befabricated from the same material as the sheath, or may use differentmaterials that optimize the reflective properties of the elements. Sincethe cavitation energy reaches a maximum at nodes along the probe, theinterval of the nodes being determined by the ultrasonic frequency atwhich the generator operates, the spacing of the reflective elements inthe sheath is determined by the intended operating frequency of theultrasonic device. Similarly, the number of nodes along the probe 22, isdetermined by the length of the probe and the frequency. As such, thenumber of reflective elements is determined by the length of the probeand the operating frequency. For example, an ultrasonic device operatingat a frequency of approximately 25 kHz employing a probe with a lengthat the thinnest interval 22 of about 3 centimeters, will display aboutseven nodes approximately 2 millimeters wide, spaced about 2 millimetersapart. Energy will radiate circumferentially around the probe at thesenodes. A sheath useful with such a probe would comprise, for example butnot limited to, a cylindrical sheath about at least 3 centimeters inlength further comprising seven reflective elements, approximately 2millimeters wide, spaced about 2 millimeters apart, positioned withrespect to the probe such that the reflective elements 118, are centeredover the nodes. Since the energy emitted by the probe radiatescircumferentially from a node, the reflective elements can extendradially from the interior wall of the sheath into the sheath lumen, forexample, 270 degrees around the interior of the sheath, while theremaining 90 degrees has no reflective element and thereby provides ameans for channeling the cavitation energy from the node to a positiondistal to the node. The channeling means of the present example may be aregion where no reflective element is present, or where the shape orangle is altered compared to the reflective element, or any other suchmeans of directing energy from the area of the node to a position distalto the node.

The sheath of the present invention may comprise a means of viewing thesite of probe action. This may include an illumination means and aviewing means. In one embodiment, the sheath of the present inventioncomprises a means for containing or introducing (if external to thesheath) an endoscope, or similar optical imaging means. In anotherembodiment of the invention, the ultrasound medical device is used inconjunction with an imaging system, for example, MRI, or ultrasoundimaging—in particular color ultrasound. In this embodiment, the actionof the probe echogenically produces a pronounced and bright image on thedisplay. The sheath in this embodiment shields the probe, therebyreducing the intensity of the probe image and enhancing the resolutionof the image by decreasing the contrast between the vibrating probe andthe surrounding tissues.

In yet another embodiment, the sheath assembly of the present inventionmay be provided along with an ultrasonic probe in the form of a kit. Inthis aspect, the probe for a particular surgical procedure is providedalong with the correct sheath, as well as instructions for assemblingand tuning the probe, and the appropriate frequency range for theprocedure. The probe and sheath may be packaged preassembled, such thatthe probe is already contained within the sheath and the respectiveposition of the probe within the sheath is optimized such that anyreflective elements in the sheath would be correctly aligned with theprospective position of the nodes for a given frequency, the kit furthercomprising instructions for the appropriate frequency. The kit mayfurther comprise packaging whereby the probe and sheath arepresterilized, and sealed against contaminants. In a preferredembodiment, the probe and sheath is provided in a container thatcomplies with regulations governing the storage, handling, and disposalof sharp medical devices. Such a container is capable of receiving andsecuring the probe and sheath before and after use. In one aspect, thesharps container provides a means of affixing the probe and sheathassembly to an ultrasonic medical device without direct manipulation ofthe probe and sheath assembly, and a means for removing the assemblyfrom the ultrasonic medical device after use. In another aspect, the kitcomprises a probe and sheath assembly contained within a sterile sharpscontainer that further comprises a single use locking means, whereby theprobe and sheath assembly is affixed to the ultrasonic medical devicesolely through the sharps container, are removed from the device solelythrough the container, and once removed can not be re-extracted from thesharps container.

Referring now to FIG. 1, a transverse mode ultrasonic medical devicecomprising an elongated probe 6 which is coupled to a device providing asource or generation means for the production of ultrasonic energy(shown in phantom in the Figure as 66) constructed in accordance withthe present invention is illustrated. The generation source may or maynot be a physical part of the device itself. The probe 6 transmitsultrasonic energy received from the generator along its length. Theprobe is capable of engaging the ultrasonic generator at one terminuswith sufficient restraint to form an acoustical mass that can propagatethe ultrasonic energy provided by the generator. The other terminus ofthe probe comprises a tip 22, which has a small diameter, enabling thetip to flex along its longitude. In one embodiment of the invention, theprobe diameter decreases at defined regional or segment intervals 14,18, 20, and 22. Energy from the generator is transmitted along thelength of the probe, causing the probe segments 22 and 23 at the distalend to vibrate in a direction that is transverse to the probelongitudinal axis. In this embodiment, one of the probe intervals 18 hasat least one groove 45 for engaging the locking assembly of a probedisposal container.

Referring now to FIG. 2, the terminal segment 22 and tip 23 of the probeare illustrated, wherein transverse vibration caused by application ofultrasonic energy to the probe generates alternating areas of maximumvibration, or “nodes” 24, along the length of the probe segment 22 andtip 23, and “anti-nodes”, or areas of minimum vibration 25, at repeatingintervals along said segment and tip. The number of nodes, and theirspacing along the probe depends on the frequency of the energy producedby the ultrasonic generator, while the separation of nodes andanti-nodes is a function of harmonic intervals of the frequency, and canbe affected by tuning the probe. In a properly tuned probe, theanti-nodes will be found at a position exactly one half of the distancebetween the nodes. Tissue-destroying effects of the device are notlimited to regions coming into direct contact with probe tip 23, butrather, as the probe is moved through the area where ablation isdesired, tissue is removed in areas adjacent to the multiplicity ofnodes produced along the entire length of the probe. The magnitude ofthe cavitation energy produced by the probe tip is such that it extendsoutward from the probe tip at the nodes from about 1-2 millimeters.

Referring now to FIGS. 3a-g, sheath assemblies comprising differentconfigurations of dampening sheaths for the ultrasonic probe 6 areillustrated. FIG. 3a shows a transverse mode probe 6 is shown comprisinga semi-cylindrical sheath 107, which partially contains the probe. Forpurposes of illustration, the probe 6 is visible beneath the sheath. Thesheath 107 is of a sufficient diameter, so as to at least partiallyencompass the probe. In the semi-cylindrical embodiment shown, thecircumference of the sheath is approximately 180 degrees, and the lengthis sufficient to span a plurality of intervals 20 and 22 over the probe.FIG. 3b shows a semi-cylindrical sheath 107 (also shown in FIG. 2), anda second concentric sheath 108 that is cylindrical, and is capable ofcontaining the first sheath 107, as well as the probe 6. FIG. 3c showsthe sheath 121 having a cylindrical structure of a sufficient diameterto contain the probe 6, made visible for the purpose of illustration.Sheath 121 comprises at least one fenestration 111, which allows thecavitation energy emitted from the probe tip to be communicated to anarea outside the sheath, through the said fenestration; probe energyfrom areas wherein the probe is not exposed by a fenestration iscontained by the sheath. FIG. 3d shows the hollow cylindrical sheath 121containing a plurality of arcutate fenestrations 111. FIG. 3eillustrates a longitudinal view of probe 6 contained within a sheath 121which comprises a plurality of arcutate fenestrations 111, and at leastone acoustic reflective element 122, that is adapted to the interiorsurface of the sheath. FIG. 3f shows a sheath 121 further comprising twosemi-cylindrical halves 109, each half connected to the other by one ormore connecting means 113. The probe 6 is capable of being substantiallycontained within the sheath. The cavitation energy generated by theprobe tip 22 is contained by the semi-cylindrical halves 109, where theyocclude the probe tip. FIG. 3g illustrates a sheath further comprisingof at least two cylinders 104, each cylinder connected to the other byat least one connecting means 113. The probe 6 is capable of beingsubstantially contained within the sheath. The cavitation energygenerated by the probe tip 22 is contained by cylinders 104, where theyocclude the probe tip.

Referring now to FIG. 4, a segment 20 of a probe is substantiallycontained in a sheath 121 comprising a plurality of fenestrations 111.Release of cavitation energy emitted by the probe 20, to the environmentis controlled by sheath 121 and is communicated to the outside of thesheath through the fenestrations.

Referring now to FIG. 5, the distal end of the probe of ultrasonicmedical device contained in a sheath assembly is illustrated. The probe6 is substantially contained within a cylindrical sheath 121 capable ofmodulating the energy omitted by an active probe, and shielding tissuesfrom puncture from a sharp probe tip. The sheath 121 shown in thisillustration has been modified such that one of the terminal ends of thesheath is substantially open, defining a fenestration or aperture 111,which exposes the probe tip 22 and 23. The terminus of the sheath 129 isshaped to provide a means for manipulating tissue to bring it intoproximity with the probe 22 and 23. A second concentric cylindricalsheath 108 which surrounds a portion of the first sheath 121, that canbe manipulated longitudinally along the first sheath to provide a meansfor modulating the exposure of the probe tip 22 and 23 by partialclosure of the aperture 111, thereby modulating the cavitation energyemitted by the probe to which occlusion materials will be exposed.

Referring now to FIG. 6, a longitudinal cross-section of a portion of anultrasonic probe tip 22 and 23 is shown, comprising a central irrigationpassage 17, lateral irrigation lumens 19, and as external aspirationchannels 60.

Referring now to FIG. 7, a transverse cross-sectional view of a portionof the ultrasonic probe shown. The probe 6 comprises a plurality ofarcutate channels 60 that extend over the longitudinal length of theprobe tip, providing a conduit for irrigation and or aspiration oftissue debris and fluid.

Referring now to FIG. 8, a sheath comprising a fenestration 111 allowingcommunication of the cavitation energy emitted by the probe to theoutside of the sheath is shown. The interior of the sheath furthercomprises reflective elements 118, shown as a plurality of planarsurfaces that extend from the interior wall of the sheath into thelumen, thereby providing a means for focussing and redirectingcavitation energy emitted by the probe tip. In this embodiment, theterminus of the sheath 129 is shaped to provide a tissue manipulationmeans.

Referring now to FIG. 8, a sheath comprising a fenestration 111 allowingcommunication of the cavitation energy emitted by the probe to theoutside of the sheath is shown. The interior of sheath 121 containingthe probe 22 and 23 comprises reflective elements 118 that are arcutate,and contain a plurality of fenestrations 111.

Sheath materials useful for the present invention include any materialwith acoustical or vibrational dampening properties capable ofabsorbing, containing, or dissipating the cavitation energy emitted bythe probe tip. Such materials must be capable of being sterilized by,for example, gamma irradiation or ethylene oxide gas (ETO), withoutlosing their structural integrity. Such materials include but are notlimited to, plastics such as polytetrafluoroethylene (PTFE),polyethylene, polypropylene, silicone, polyetherimide, or other suchplastics that are used in medical procedures. Ceramic materials can alsobe used, and have the added benefit that they may be sterilized byautoclaving. Combinations of the aforementioned materials can be useddepending on the procedure, for example as in the sheath of FIG. 5, aceramic sheath 121 can be used in combination with a moveable PTFE outersheath 108. Alternatively a single sheath may employ two or morematerials to give the desired combination of strength and flexibility,for example, the sheath may comprise a rigid ceramic section distal tothe probe tip 23 and a more flexible plastic section proximal to thetip, capable of flexing with the probe 22. In the currently preferredembodiment of the invention, PTFE is used to fabricate a strong,flexible, disposable sheath that is easily sterilized by irradiation orETO gas.

It should be obvious to those of ordinary skill in the art that theindividual features described herein may be combined. Variations,modifications, and other implementations of what is described hereinwill occur to those of ordinary skill in the art without departing fromthe spirit and scope of the invention as claimed. Accordingly, theinvention is to be defined not by the preceding illustrative descriptionbut instead by the spirit and scope of the following claims.

We claim:
 1. An ultrasonic device for tissue ablation comprising: an elongate probe body having a proximal end, a distal end and at least two regions of differing cross-sectional dimension; an oscillating flexible probe tip at the distal end of the probe body having a cross-sectional dimension smaller than the proximal end; a transducer contained in a probe handle capable of vibrating at an ultrasonic frequency coupled to the probe body; an adapting mechanism mechanically coupling the transducer to the probe body to enable translation of vibrations from said transducer to the probe, causing a length of the probe body including the probe tip to be oscillated transversely to its longitudinal axis; and a sheath assembly adapted to said probe comprising at least one sheath, wherein the probe body emits a transverse ultrasonic energy along the length of the probe body so that a plurality of transverse nodes and anti-nodes are formed along the length of the probe body.
 2. The ultrasonic device of claim 1 wherein the sheath assembly covers at least a portion of the probe, said sheath assembly comprising a longitudinally extending structural wall that defines a longitudinally extending hollow interior for accommodating at least a portion of said probe, wherein said structural wall of said sheath assembly is substantially self supporting so that the said structural wall maintains substantially the same shape with said probe disposed in the said hollow interior as without said probe disposed in the said hollow interior.
 3. The ultrasonic device of claim 1 wherein the sheath assembly substantially prevents transmission of cavitational energy generated by the probe to the surrounding environment.
 4. The ultrasonic device of claim 1 wherein the sheath assembly further comprises at least one fenestration.
 5. The ultrasonic device of claim 4 wherein the fenestration is capable of transmitting cavitation energy therethrough to surrounding environment.
 6. The ultrasonic device of claim 1 wherein the sheath assembly further comprises one or more devices capable of manipulating tissue.
 7. The ultrasonic device of claim 1 wherein the sheath assembly further comprises at least one reflective element.
 8. The ultrasonic device of claim 1 wherein said sheath assembly further comprises at least one irrigation channel.
 9. The ultrasonic device of claim 1 wherein said sheath assembly further comprises at least one aspiration channel.
 10. The ultrasonic device of claim 1 wherein said sheath assembly further comprises at least one channel for delivering a therapeutic agent therethrough.
 11. The ultrasonic device of claim 1 wherein said sheath assembly further comprises an imaging device.
 12. The ultrasonic device of claim 1 wherein the sheath assembly is adapted for use with an imaging system.
 13. The ultrasonic device of claim 1 wherein the device is part of a kit for removing an occlusion in a vessel, and said kit further comprising a container capable of retaining the said probe and sheath assembly, and appropriate packaging to contain and maintain the sterility of the contents.
 14. A kit of claim 13 wherein the ultrasonic device and sheath assembly are pre-assembled in a preferred configuration.
 15. A method of modulating, focusing and directing cavitation energy emitted from a ultrasonic probe coupled a transducer capable of providing an ultrasonic excitation signal to said probe, vibrating in a transverse mode for tissue ablation comprising: enclosing at least a portion of the probe within a sheath assembly having at least one fenestration; inserting the probe of an ultrasonic medical device into a blood vessel; guiding the probe and the enclosing sheath assembly into the blood vessel up to a site of an occlusion; positioning said probe and the sheath assembly such that the fenestration is in proximity with the occlusion causing materials; providing an ultrasonic electrical excitation signal to said ultrasonic medical device and transferring the signal along a length of the probe to a flexible probe tip, thereby causing transverse vibration of the length of said probe and the generation of a plurality of nodes of a cavitation energy along the length of said probe; and controlling the selective transmission of the cavitation energy through the fenestration in the sheath assembly, thereby directing said energy specifically in an occluded area within the blood vessel to cause fragmentation of the occlusion causing materials.
 16. The method of claim 15 wherein the sheath assembly is capable of partially shielding the tissues at the site of a surgical procedure from said probe.
 17. The method of claim 15 wherein the sheath assembly further comprises an aspiration conduit, whereby fragments of the occlusion causing materials are removed through said conduit.
 18. The method of claim 15 wherein the sheath assembly further comprises an irrigation conduit, and enabling supply of an irrigating fluid to the site of the occlusion causing material removal.
 19. The method of claim 15 wherein the sheath assembly further comprises a conduit for delivering a therapeutic agent therethrough.
 20. The method according to claim 15 wherein the sheath assembly further comprises an imaging system enabling positioning of said probe proximal to said occlusion.
 21. The method of claim 15 wherein the sheath assembly further comprises a tissue manipulation device.
 22. The method of claim 15 wherein the sheath assembly shields ultrasound energy emitted from said probe thereby increasing the resolution of said surgical site when visualized by an ultrasound imaging system.
 23. The method of claim 15 wherein the sheath assembly is used for guiding the ultrasonic probe to a surgical site further comprising: introducing the sheath assembly from an exterior of a patient to the site of the occlusion, and introducing the ultrasonic probe into said sheath assembly. 